Stereographic photograph of children playing hopscotch in Jammu and Kashmir, taken by James Ricalton in c. 1903, from The Underwood Travel Library: Stereoscopic Views of India. This is one of a series of 100 photographs that were designed to be viewed through a special binocular viewer, producing a 3D effect. The series was sold together with a book of descriptions and a map with precise locations to enable the 'traveller' to imagine that he was touring around India. Stereoscopic cameras, those with two lenses and the ability to take two photographs at the same time, were introduced in the mid 19th century and revolutionised photography. They cut down exposure time and thus allowed for some movement in the image without blurring as subjects were not required to sit for long periods to produce sharp results.